Spark plug



March l 1927.

P. CHAI-LIS SPARK PLUG Filed Feb. 27, 1922 2 sheets-Sheet 1 Il( Illllllllllll) '94 March 1-, 1927.

1,619,653 P. CHALLS s'PAzK PLUG Filed Feb. 27, 1922 2 ,Sheets-Sheet 2 mme@ Patente'd Mar. 1, 19727.

UNITEDo STATES 1,619,653 PATENT FFICE.

Parmiemanare, or vrc'ronm, LoNDoN, ENGLAND.

SPARK PLUG.

Application led February 27, 1922, Serial No. 539,539, and in Great Britain March 17, 1821.

This invention relates to spark plugs for internal combustion engines, and consists in a novel and simplified constructionof plug, which while aording a reduction in the number of constitutent parts employed gives improved results in working, renders the flame of the explosion visible and is readily taken apart so that every piece canbe easily cleaned and reassembled or replaced.

Means are also provided for adjusting the width -of the gap between the discharge points and for cooling the central electrode to prevent overheating, the maximum cooling effect for the central electrode being afforded by allowing lateral access of air thereto through the plug-barrel.

The inventlon is hereafter described withI reference to the accompanying drawings7 in which Figure 1 is van elevation and Figure 2 is a longitudinal section of the plug, according to the preferred construction.

Figure 3 is a cross-section online 3 3 of Figure 2. 4

Figure 4 is a detail section, corresponding to Figure 2 and showing an alternative form of support for the outer end of the electrode.

Figures 5 and 6, 7 and 8, 9 and 10, and 11 3 and 12, show various arrangements forad just-ing the gap at the spark electrodes.

.The lug-barrel a has .the 'usualscrewthreaded extremity a carrying or providing the outer electrode in suitable relation to the central insulatedele`ctrode g.. The plug'4 is bored out at itsend ato receive an insulatoi` b made preferabl 'of silicaior quartz and of comparatively s ort length; this in'- sulator has a conical shoulder bf approxi- 40' mately midway of`its length. fitting upon a corre ondingly ,oblique seating a2 in the plug-bo y, the 'two conlcal surfaces providlng a as-tight joint, for example by being.,r groun or -otherwise accuratel iinished,

without 'requiring packing was ers. The head. g of the central electrode andthe f lower end of the insulator b also engage each other on a similar but reversed-angle is preferabl insulator to seat itself freely under longitudinal movement while yet allowing it to return when the central electrode stem or head contracts and when the circumferential .shrinkage of the plug-body reduces the diameter of the seating in rela-tionto that of the insulator. Any breathing movements or differences in expansion and contraction during working of the plug are fully met in this way without danger of crushing the insulator, as would occur in the case ofa similar insulator having a conical shape of finer taper.

- The outer end of the plug-body is formed as a thin tubular extension b2 which encloses an air-space, and the'walls of this tubular portion are drilled or apertured as at Sto reduce the mass and facilitate the circulation of air laterally into or from said space. AThe usual hexagonlc for manipulation may be provided at any convenient position upon the plugbody..

At the outer end of the plug, the u per .insulator .d rests u on'a supporting ga lery e, the tubular portion. b2 ofthe lug being counterbored tu, provide a shou der b* on which gallery lis supported.

The central electrode consists of a metal rod g screw-threaded at one end and pro*7 vided at the other with a fiat or mushroom head g which rests b means of a reversed conical seating upon t e lower surface of the silica insulator I), and is knurled or toothed around its periphery g2 so as to aiford multiple sparkga s vbetween said head and the extremity of t e screw-threaded shank a.

v The stem ofthe central electrode, passes through an axial hole in the silica insulator b, is exposed to the air-space wit-hin the tubular portion b2, and then enters. an axial 4holelin the upper insulator d, above which it 'is Yiittedffsee Figure 2) with .a springwasher vg",,lock-nut g4 and terminal nut g. Alternatively a sprin gallery may be employed, as shown in igure 4, consisting of a dished spring washer e', the elasticity of which com ensates for the expansion or contraction vo all the arts ofthe plug; thus in this constructiont e spring washer ga and lock nut g4 are not requiiied.

To increase its radiating surfacathe ex- Y posed-length of the central electrode stem `which may e a continuation of that at its formed with a screw-thread,`

outerend. Alternatively the stem may be V fitted with other radiatlng means. .I haveshown for example a coolin vane` h made of aluminum screwed aroun the stem, this vane having wings it to increase the radlating surface. The wings can, with advantage, be arranged to project radially of the plug towards the rectangular windows b5 in the barrel of the plug. As the addition ofthe vane h to the central electrode reduces its distance from the tubular extensionA b2 o f the plug-body, I fit` a liner f, preferably of mica, with openings f reglstering with but of smaller area than the apertures marked b3 in the plug-body. This insulating liner maybe held in position by the downturned peripheryof the gallery e, as shown in Figure Apertures e2 ma be provided to allowT aircirculation to or. om the air-space. Since the -upper insulator is freely exposed to the air for cooling and since the heat is dissipated from both the central electrode stem and the plug-barrel before reaching lthe points where these parts make contact with the outer insulator, the temperature of the latter never attains a high figure. Thus it is feasible to employ even materialsuch as vulcanized fibre for this insulator, though other insulating materials, such as steatite, porcelain and bakelitewill be preferable.

Similarly as the tubular lportion of the plug-body is so amply cooled by the air circulation through its apertured sides, the hexagon at its upperend remains com-paratively cool and 1t is possibleto handle the plug without hurt, even when freshly re- `moved from a working cylinder.

It will be noted that the only joints subject to working pressure are the conical seatthe silica insulator and the plug-body and between the lower end of the silica insulator and the central electrode head. Since these can be formed as ground joints without packin material, the plug may be repeatedly ta en to pieces for cleaning or replace. ment of components without prejudice to its gas-tightness when reassembled. More- OYQP the 10W temperature at which the cenf tral and outer parts are maintained reduces '-'the amount of expansion and contraction,

so that the detrimental consequences of such movements in other plugs are suppressed, while at the same time the design 'of thev parts enables them better -to withstand the movement.' The spring washer or its'equivalent mounted upon the electrode stem serves to tension or,l oad the latter in an elastic manner and ASince the head gf ofthe centrahelectrode i 'rests or beds upon the lower surface or outer end of the silica insulator, by means of a reversed 'conical seating, as'already stated,

under the tension of the spring, the central for all expansion andi -"may occur 1n every part 1n periphery shaped with a series of cams or spiral -curves j; the periphery of the central electrode head is formed either with an equal number of lugs or projectionsz (Figures 5 and 6) or as inFigures 7 and 8) 'with a series of cams i corresponding in pitch with those of the ring. By partially rotating the central electrode, the sparking distance between the outer electrode and the projections z' or cam faces i may be varied between limits determined by the rise or the spirals. The nickel ring may be secured to the plug-shank by being fitted in a counterbore jg of depth slightly greater than the thickness of the ring, the overhanging wall being then turned down, beaded or un over the ring to secure the latter in positlon. In another construction, shown in Fig ures 9 and 10, the head g of the central eleci trode carries a plurality of radial arms or lugs, the lip ofthe plug-shank having corresponding projections or castellations js; the gap between the two sets of projections can thus be adjusted by partly rotating the central electrode. ings between the intermediate shoulder of Figures 11 and 12 illustrate another modication in which a ring j* of nickel or Athe like is pressed into an annular groove j in the interior of the shank a', the section of the. groove being either curved or rectangu lar as shown at the two sides'of' the shank respectively in Figure 12. The ring is pro vided with arms je extending parallel to the axis in suitable relation to the central electrode head g. v Y

.An important result obtained by the use of a silica insulator and by' the open construction of the outer portion of the plug, is that the electrical discharge at the plug electrodes .and the flame of the explosion can easily be seen through the apertures. This enables the plugs to be checked by mere inspection when misfiring is suspected, and

also enables carburetor and other adjustments to be made by an unskilled operator since the results of the adjustments are im mediately visible bythe change in colour of the explosion Haine. Further the provision of the serrated or knurled'head of the central electrode results in oil which? may be.

thrown on the said head sinking into the spaces between the adjacent teeth without lknurled or serrated head and thereby pro- Y voking short circuits.

What I claim is 1. A spark-plug, comprising a tubular body, one 'end of, said body being adapted for connection to an engine cylinder and bored to provide a seating; an insulator seated within the bored end of 'saidbody, an electrode passing through said insulator; a second insulator surrounding the stein of said electrode, said stem being exposed between the adjacent edges of said insulators,

an apertured support for said second insu? lator, said support resting upon said body; said tubular body being apertured to allow access of air to the exposed length 'of said electrode within said bod and between said insulators; said support eing apertured to "alloiv passage of air from within said body and means or holding the parts in position.

2. A spark-plug, comprising a tubular body; a hollow insulator made of silica mounted in said body; an electrode passing through said insulator and having its head mounted thereon; a second insulator surrounding the stem of said electrode; an apertured support for said second insulator, said support resting upon said body, the apertures in said support being so placed as to allow observation'therethrough of illumination transmitted through said silica i11 sulator; and means for yholding the parts in position.

In testimony whereof I hereunto aiiix-my signature.

PHILIP CHALLIS. 

